This invention relates to Lewis Base Bridged intermetallic compounds of transition metal-reducing metal complexes, especially as prepared from transition metal oxide alkoxides. More particularly, the invention affords catalyst precursors for interreaction with halide activators to provide a catalyst component adapted for the polymerization of alpha olefins.
Polyethylene, produced by solution or slurry processes at lower pressures providing a linear high density resin, or in autoclave or tubular reactors at higher pressures, providing a long chain branched low density resin, has been an object of commerical production for many years.
It has been recognized that certain characteristics of the linear high density resins such as stiffness and abrasion resistance would usefully be combined with valuable properties of the branched low density resin such as high impact toughness and stress crack resistance, and it has been discovered that the interrelationship of these properties may be attributed in part to the nature and amount of side chain development.
Accordingly, linear low density polyethylene resins have now been produced in low pressure processes employing specialized catalyst systems, the resins being characterized by linearity and short chain branching afforded by alkene comonomers (without significant long chain branching), and offering narrow molecular weight distribution, improved strength properties, higher melt viscosity, high softening point, improved ESCR (Environmental Stress Crack Resistance) and improved low temperature brittleness. These and related properties provide advantages to the user in such applications as blown film, wire and cable coating, cast film, co-extrusion, and injection and rotational molding.
It is an objective to manufacture such linear low density resins in an economic and efficient manner under the conditions in existing reactors, and to accomplish such manufacture with the provision of resin of competitive product characteristics, employing catalyst systems having user acceptable residues.
The linear olefin polymers have typically been produced using coordination catalysts of the general type disclosed by Ziegler, thus comprising a transition metal compound, usually a titanium halide admixed with an organometallic compound such as aklyl aluminum. The transition metal component may be activated by reaction with a halide promoter such as alkyl aluminum halide. Among the improved catalysts of this type are those incorporating a magnesium component, usually by interaction of magnesium or a compound thereof with the transition metal component or the organometallic compounds, as by milling or chemical reaction or association.
It is a further object to provide a catalyst for the polymerization of alpha olefins affording a range of resin properties under various synthesis conditions.
A particular object is the preparation of linear low density polyethylene having a broadened molecular weight distribution.